Numerous operations associated with mining and post-mining purification of minerals extracted from mines have traditionally been performed manually and without the use of automation, such as with robots. These operations span all aspects of mining, from extraction to metal purification, including processes associated with smelting, electrodeposition, electrorefining, cleaning, and disposal. These operations also include operations associated with maintenance of equipment, such as furnaces and smelters, so as to improve efficiency, cost, or improve safety for operators. The present invention is directed to automating portions or all of these manual processes through the use of robotic systems.
Extractive mining is the science of extracting metals or other products with metallic content from mines. In other words, mining includes the way in which minerals are retrieved from the ore deposit, treated inside the mine, and how they are transported to a plant, and subsequent processed.
Copper ore occurs in two basic forms in nature: sulfide ore and oxide ore. Sulfide ore normally contains a combination of copper, sulfur and iron, and is generally found far below the surface. Oxide ore normally occurs closer to the surface, and contains copper and other minerals in oxide form.
The mining process is specific for the kind of copper ore that is being processed, as shown in FIG. 1. In general, Exploitation is either underground 710 or open pit 712. The exploited matter is then moved to crushing 714. For sulfide ore, the next step is grinding floatation 716, which is followed by smelting 718 and electrorefining 720, or molybdenum roasting 722. For oxide ore, a lixiviation and solvent extraction process 724 is performed followed by electrowinning 726.
Exploitation
The objective of this stage is to extract the rock containing copper and other minerals and transport it to the processing plant in an efficient and safe mode. This usually involves fragmenting the rock to remove it from its original position and to achieve a size that is manageable for transportation and handling.
There are two types of exploitation methods. “Open pit” exploitation includes a set of operations to extract rock or mineral with economic value through retrieval of minerals recovering in a partial or complete way from the surface. In “underground” exploitation, access tunnels are built to reach an underground mineralized vein or other mineral deposit. In both methods, rock retrieval is generally performed through the use of explosives. The transportation of the extracted mineral is usually achieved using trucks or trains.
Train wagons and trucks go through periodic cleaning as material from the mine tends to adhere to the surface, diminishing their load capacity. Carrying out this activity presents a physical effort for those who perform it, with a high accident risk rate. Another important aspect is the time this activity takes, which means less availability of the equipment which results in productivity losses. Generally speaking, the failure of the ability to wash the wagons on a regular basis impacts mining capacity, equipment availability, safety, and cost.
Crushing
The ore extracted from the mine is usually considered not suitable for industrial treatment due to the uneven level in the granulometry. Thus, it is necessary to reduce the size of the ore to a suitable size, which is carried out in different stages of particle size reduction such as crushing and grinding, and according to the reduction level required.
The crushing process is intended to reduce the size of the ore and obtain a uniform size of particles, prior to grinding. Crushing often occurs in three stages in series that sequentially reduce the size of particles. These are known as primary, secondary and tertiary crushing, respectively. Nevertheless plants incorporating semi-autogenous grinding (SAG) mills only require primary crushing. Crushing generally occurs in the plant located in the vicinity of the mine, but in underground mines primary crushing may occur inside the mine.
Transportation between the different crushing stages is generally achieved using conveyor belts. The output of each crusher is stored in stock piles that guarantee a constant flow of material to subsequent stages. This constant flow of material is critical to certain types of crushers and SAG mills.
In underground mining it is common to find residues from old exploitations such as pieces of metal and wood. These external elements commonly enter the mineral flow, causing the crusher to clog. Clogging might also occur when excessively large lumps are present in the mineral flow. All clogging episodes require manual intervention for unblocking and cleaning. To carry out this activity demands a physical effort and is a risky operation for the personnel in charge, with the subsequent risk of a fatal accident for those carrying out the activity. Another important aspect is the reduced availability of the equipment and costs associated to personnel performing the task, leading to great losses of productivity.
Sulfide Ore: Grinding and Flotation
The product of the crushing process enters the grinding stage. Grinding mills carry out the mineral comminution process (i.e. the particle is broken to a smaller size). This process is carried out by combining impact and usually in a water suspension. There are two different grinding technologies: conventional and SAG grinding.
Conventional grinding is normally performed as a sequential process involving two different mills: a bar mill and a ball mill, respectively. The former uses steel bars which freely flow and fall over the material. The later uses steel balls as the main grinding agent, reducing the material to a size of less than 200 microns which is then used in the flotation process. Many modern plants only include a ball mill in the grinding stage.
SAG grinding involves a larger and more efficient kind of mill compared to conventional grinding. The system is fed with material from the primary crusher, which grinds the material using steel balls that usually occupy the 12% of the capacity of the mill. The size of the resulting material is in the order of microns, which can be used in the flotation process.
Grinding machinery is provided with liners which are generally used for internal covering of the grinding machines. The inner wall of such machinery is subjected to impact and abrasion resulting from material circulating inside, which leads to a constant wear of the surface. In order to absorb this permanent wear and not to damage the frame of the equipment, sacrifice parts are installed, which are intended to improve the process through geometrically favoring the abrasion and impact among the particles in the equipment. These parts need to be replaced regularly so as to avoid permanent damages to the equipment frame. As part of the maintenance process, bolts which fasten the liners in place should also be removed manually with hydraulic tools.
One of the major disadvantages of the current methods used for bolt removal is the long maintenance time, which generates a loss in equipment productivity due to the fact production is reduced because of mill stoppage. Another disadvantage of the current methods for bolt removal is safety, due to the fact the personnel often need to go inside the equipment to remove the bolts, which is usually a risky operation, mainly due to the fact some elements which are trapped between the liners fall down.
As part of the normal operation process of grinding mills, grinding balls are automatically loaded into a mill. However, an automatic loading unit regularly clogs and the reactor must be loaded manually. Similarly, the low storage capacity requires continuous use of a crane.
The grinding process has the major disadvantage of being a lengthy operation, which results in a loss in equipment productivity because production is reduced because of mill stoppage. Another disadvantage of the current method for ball loading relates to safety. Sometimes personnel must enter the equipment, which is usually a risky action, mainly because some elements which are trapped between the liners fall down. Due to the above, a robot system and method have been developed which allow for an automated ball loading process into grinding mills, so as to diminish the time spent for ball loading and to reduce risk of accidents in the personnel.
Flotation corresponds to a physicochemical process which separates the valuable minerals (copper and molybdenum) from other materials. The pulp from the grinding process is deposited in “flotation cells” which contain a mixture of mineral, water, reagent materials and other special additives. The mixture is kept in constant agitation using a flow of air, causing bubbles. These bubbles carry the sulfide minerals to the surface, exceeding the height of the flotation cell and then flowing to special tanks. This mixture is known as “copper concentrate”, which contains over 30% copper.
Sulfide Ore—Molybdenum Roasting
Besides the copper concentrate, the flotation process also provides a molybdenum concentrate byproduct (molybdenum disulfide MoS2) which is processed to obtain technical molybdenum oxide. Molybdenum corresponds to a valuable sub-product obtained by the copper production process of the sulfide ore.
The molybdenum concentrate is characterized by a darkish and very slippery fine dust which is subjected to a process called roasting to eliminate sulphur. Molybdenum concentrates are roasted in level furnaces at temperatures over 650° C. to produce technical molybdenum oxide with a fine molybdenum content of about 57%. The resulting product is technical grade molybdenum trioxide, which is a greenish yellow dust. It is sold packed in drums, small drums or in briquettes in maxi bags.
During the operation of the roasting furnace, the levels are cleaned on a regular basis, which is intended to eliminate the accretions build up and adherence to different parts of the furnace, such as due to material cooling and/or a change in the chemical composition. The cleaning process is carried out by operators of the shift and each operator cleans four levels.
For the purposes of quality control, humidity, product grade, and the weight of the unit to be transported need to be determined by sampling. In particular, molybdenum sampling is frequently performed directly from the maxi bags in a manual fashion. This results in low representativeness of the samples obtained.
Sulfide Ore: Smelting
The copper concentrate from the flotation process is placed in smelting furnaces for purifying and extracting valuable portions of the ore, where casting is performed at temperatures over 1,200° C. The metal of interest is sequentially cast and refined through several stages which results in a high purity metal.
The first stage of the process is drying up the copper concentrate using filters. The dried concentrate is then taken to a smelter furnace which takes the concentrate to a liquid state. Smelter furnaces can be of two types: tilting furnaces (e.g., Teniente and Noranda furnaces) or Flash furnaces (e.g., Isasmelt and Ausmelt furnaces). These furnaces generally use heat generated by oxidation reactions at high temperatures to separate metals and/or concentrated into two collections of matter: (1) matter rich in valuable metal, called matte, and (2) matter poor in valuable metal, called slag. The slag is floated over the matte.
In general terms, smelting furnaces operate on a continuous basis with ore being introduced using a reception ladle, while the separate matte and slag are unloaded to bins through batch processes, which may be carried out manually by operators and involves punching a passage within the slag to be used as an outlet channel so that the slag may be discharged, sampling the slag for testing so as to assure proper furnace operation, plugging the passage in order to close the slag exit, and cleaning channels to remove the slag solidified by its passing through the outlet channel to the bin. In order to load and unload the furnace, doors to the furnace are regularly opened and closed. The slag generated from this smelting process may be fed to an electric furnace for treatment before disposal. For these purposes, the slag from these furnaces is constantly unloaded manually through use of a reception ladle. That is, a reception ladle sized to the furnace opening (to limit heat loss) is manually introduced into the furnace to scoop slag for removal. When the slag cools off, it solidifies and adheres to the reception ladle, which essentially grows the ladle, which both reduces the size of the ladle's scooper and expands the ladle such that it may no longer fit the opening of the furnace. This results in a slow down for the manual unloading and unloading processes, in order to allow time for cleaning ladles. One of the main additional disadvantages of the tasks associated with cleaning ladles is the exposure of the personnel to harsh environmental conditions. This, in the medium and long term could generate serious occupational diseases to the operators in charge of carrying out this task.
The second stage of the process takes the matte (i.e. copper content of approximately 60%) into a Peirce-Smith converter, to obtain blister-type copper with over 96% copper.
In the third stage a fire refining process is carried out in a refining furnace to increase the purity of the blister-type copper by eliminating its oxygen components. The resulting product contains a copper purity of over 99%. When the metal load reaches the required purity level, the furnace is inclined and the metal is poured into anode molds in a fire-refined mold casting wheel. Once the metal is poured into the mold, the wheel rotates to advance the following mold to the next position and another anode is molded. To finish the smelting process, the dislodging process (stripping and/or extraction) lifts the molded anodes and sends them to a cooling tank to avoid excessive oxidation and to obtain a deep scrubbing. Cast anodes are counted and arranged in predetermined bundles or arranged at distances as required by the electrolytic plant. The discharge of the cooling tanks is carried out by a forklift or other anode lifting devices.
As of the slag, this is processed in a modified Peirce-Smith converter or an electric furnace, which recovers most of the copper remains.
One of the major disadvantages of tasks associated with anode casting and cast dislodging processes from casting wheels is the exposure of personnel to harsh environmental conditions, the non-initial classification of anodes and the high rate of failures of the current take off system. The exposure could generate serious occupational diseases to the operators carrying out these activities as well as delays in the anode production. In addition, the manipulation of the tool used by the operator in these tasks must be carried out with extreme care for not damaging the surface of the cast.
Anodes commonly present burrs, ridges and other small surface defects. The task of burr and defects elimination from anodes is traditionally carried out manually or semi-automatically which causes the system to be less efficient. In turn, surface inspection has the disadvantage of being carried out visually by operators which gives a subjective classification and varies between operators.
Furthermore, operators are often subjected to high physical demand and harsh environmental conditions.
Sulfide Ore: Electrorefining
The electrorefining process transforms copper anodes from the smelting process into copper cathodes with an extremely high content of copper (99.99%).
Electrorefining is a metal purification process based in electrolysis, in which the anode is electrochemically dissolved in a cell and is deposited over a starting sheet (i.e. thin copper sheet or a stainless-steel base plate) submerged in an acid solution of copper sulphate. The resulting product is a solid copper cathode formed over the starting sheet.
At the end of electrefining there is a certain portion of the anodes that is not dissolved, and stays as residual in the cells. These remains are called scrap and are removed from the cells by a bridge crane and moved to the loading yard. In this place, the operators arrange the scrap in bundles for commercialization.
The current procedure for scrap bundling requires a great number of operators, which implies high operating costs. Similarly, the operators are exposed to a high physical demand due to the weight of the scrap, which usually reaches 70 kg. One of the major disadvantages of the tasks associated to scrap bundling is the exposure of the personnel to harsh environmental conditions. This, in the medium and long term, could generate serious occupational diseases to the people in charge of carrying out these tasks.
Oxide Ore: Leaching and Solvent Extraction (SX)
For the oxide ore the mineral goes through a different process than for sulfide ore (see FIG. 1). For oxide ores, the mineral is leached after crushing. Leaching is a hydrometallurgical process that uses a mixture of sulfuric acid and water to extract copper from the mineral.
Leaching is generally performed on “leach heaps”, i.e. piles of crushed material that usually reaches heights of 6-8 m. Leach heaps are built over an impermeable membrane and slotted tubing system, used to drain the solution that flows through the pile. A drip and spray irrigation system covers all the exposed area of the leach heap, gradually pouring a solution of sulfuric acid and water. This solution flows through the pile and dissolves the copper contained in the oxide ore, forming a copper sulfate solution that is then transported using gutters. The process takes place in 60 days, approximately. Solid particles are then removed from the solution.
After leaching, the solvent extraction (SX) stage increases the copper concentration of the copper sulfate solution by an ionic extraction. The resulting copper sulfate solution is used in the electrowinning process.
Oxide Ore: Electrowinning (EW)
The electrowinning process recovers the copper present in the solution from the SX process to produce solid cathodes with a high concentration of copper (99.99%).
The copper sulfate solution from the SX process is taken to the electrowinning cells, i.e. tanks. In each cell a sequential array of anodes and cathodes is submerged in the solution (seeding). Anodes correspond to lead plates while cathodes (“base plates”) generally correspond to a stainless steel starting plate, but may alternatively correspond to a copper starting sheet. Anodes and cathodes form an electric circuit with a low current flowing from cathode to anode. Copper molecules in the solution are attracted by the negative pole in the electric circuit adhering and becoming part of the cathode.
Cathodes are deposited in the electrowinning cell in batches for a pre-determined period of time, where they reach a determined weight. Once the weight is reached, the cathodes are retrieved (harvested) through an operation carried out by a bridge crane, which takes the volume of cathodes of each cell and moves them to a washing tunnel in which the remains of copper and organic material are removed from the cathode surface. In this stage, water and vapor are propelled through fixed nozzles on the cathode faces. In the case of plants with stainless-steel starting plates, the cathodes then pass to the stripping machine where copper is finally separated from base plates.
During cathode stripping, certain plates such as plates with metal residues, plates with low weight or overweight, bent plates or plates requiring maintenance, are rejected by the control system of the cathode stripping machine. These base plates are not subjected to an automated reposition system to the return line, so the number of plates returning to the normal operation is lower than the number of plates fed to the stripping machine, with the resulting deficit of base plates in the seeding of cells.
The repositioning of the missing base plates in the cells—as a result of the rejection being made by the control system of the stripping machine — is carried out manually and/or mechanically directly in the cells or by filling an additional rack parallel to the return line of the base plates. The rack provides the bridge crane with missing plates to complete the seeding process into the cells.
The disadvantages of the current stripping process include (1) continuous deterioration of base plates because of chemical (corrosion) or mechanical (bending, and hammering during stripping) effects, (2) base plate repairing is carried out manually with high maintenance costs and low quality levels that may affect the efficiency of the process, (3) base plate replacement and repair has high accident levels and demands important physical efforts to operators that could generate serious occupational diseases, and (4) atmosphere in an electro-winning plant is highly contaminated and presents potential risks for the plant personnel.
The disadvantages of the actual method of cathodes washing include (1) exposing washing and stripping personnel to high physical demand and harsh environmental conditions, (2) the fixed nozzles cannot impact the entire surface with the same strength, (3) any optimization being made to the nozzle stops the machine, and (4) maintenance tasks are difficult due to space problems.
Cathodes obtained as the final product of the electrowinning process have different quality levels due to the presence of several contaminants (lead and chloride among others), which lessens the purity of the harvested cathodes. Due to the contaminants, all the cathodes obtained in the electrodeposition process must be inspected and organized according to their quality. Currently this procedure is carried out manually which has some disadvantages, including (1) high physical demand from the operators due to continually manipulating heavy loads, (2) high operating costs due to the high number of people involved in the activity, and (3) low quality control due to the fact there are no objective parameter to define the different qualities of the cathodes.
The present invention overcomes these limitations by providing for methods of use of robotics so as to improve efficiency or cost, as well as to reduce or eliminate exposure of personnel to difficult, hazardous, or environmentally unfriendly work conditions.
It is an object of the invention to overcome the limitations of manual processes associated with mining by introducing preprogrammed robotics so as to improve efficiency, cost, and safety to personnel.
It is also an object of the invention to provide for an automated means of performing repetitive functions in the course of mining and mineral purification, particularly under hazardous or environmentally unfriendly conditions.
It is also an object of the invention to introduce robotics into activities associated with mining and mineral purification such that select functions may be performed remotely so as to improve safety for operating personnel.
It is also an object of the invention to introduce robotics into activities associated with mining and mineral purification such that a sequence of functions can be accomplished in an automated way, thereby improving efficiency and cost.